The Use of Isoproterenol in Electrophysiologic Drug Testing in Patients with Sustained Ventricular Tachycardia : The Mechanism and Clinical Significance of Isoproterenol
Isoproterenol has been used in electrophysiologic studies to facilitate the induction of ventricular tachycardia (VT) as well as in drug testing. However, the mechanism of the induction of VT and the clinical significance of the VT induced with isoproterenol have yet to be determined. The present study assessed the effects of isoproterenol in the induction of VT during drug testing in 23 patients (34 drug testings), and analyzed the patients' characteristics and electrophysiologic parameters. The standard protocol for inducing VT was used. Sustained monomorphic VT was induced in 15 testings after the use of isoproterenol (ineffective drug testing). In the other 19 testings, sustained VT was not induced even after the use of isoproterenol (effective drug testing). Isoproterenol altered the electrophysiologic parameters in a similar manner in the two testings. However, nonsustained VT was more frequently induced before isoproterenol in the ineffective drug testings: 60% vs 16% (P <0.05). This indicates that isoproterenol converted nonsustained VT into sustained VT, implying that isoproterenol improved the conduction within the slow conduction zone, resulting in VT which did not terminate spontaneously. Facilitated conduction outside the reentry circuit, namely, the interventing tissue between the stimulation site and the reentry circuit, likely played a minor role. The majority of patients treated with an effective drug showed no recurrence of VT during the follow-up period.
- Acta medica et biologica = Acta medica et biologica
Acta medica et biologica = Acta medica et biologica 40 (1), 35-41, 1992-03
Niigata University School of Medicine